Drilling fluid

ABSTRACT

A drilling fluid for use in high oil viscosity formations containing tar, sand and oil entrained therein. The drilling fluid can be comprised of a polymer in an amount from between 0.05% and 5% by volume, a solvent in an amount from between 1% and 20% by volume and de-emulsifier in an amount from between 0.05% and 10% by volume.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/460,878, filed Apr. 8, 2003.

FIELD OF THE INVENTION

The present invention relates to drilling fluid and more particularly, the present invention relates to a drilling fluid composition adapted for use in high oil viscosity applications such as steam assisted gravity drainage (SAGD) and soak radial wells.

BACKGROUND OF THE INVENTION

In the existing technology, there is a wide variety of documents relating to drilling fluids and related materials.

It is known that drilling fluid, also referred to as drilling mud, is an important part of a drilling operation. The fluid is important to effect transport of debris, undesirable materials, gas etc. The fluid also functions to maintain lubrication and act as a coolant of the drill bit which experiences enormous force, friction and other stresses.

Typical of the presently used fluids is Kim Mud (a blend of polysaccharide polymers, calcium carbonate, calcium lignosulfonate). This material provides high carrying capacity by an inherent thixotropic viscosity. The composition may contain potassium ions for redncing volume increases (swelling). This has the advantage of preventing hydration of moisture sensitive clays.

D-limonene has also been used in drilling fluid and is particularly favored in view of the fact that it is a natural substance extracted from citrus rind.

Various amines have also been used to augment drilling fluid and provide a variety of advantages in different operating conditions.

It would be desirable to have a fluid capable of cleaning tar out of sand and incorporate the oil in an emulsion with subsequent release. Most of the fluids in current use are based upon preventing the tar (heavy oil) from entering the mud.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved drilling fluid which is not limited as the prior art compositions.

A further object of one embodiment of the present invention is to provide a drilling fluid for use in drilling high oil viscosity formations (tar, sand and oil entrained therein), comprising:

-   -   a water base viscosifying polymer in an amount from between         0.05% and 5% by volume;     -   a solvent in an amount from between 1% and 20% by volume; and     -   a de-emulsifier in an amount from between 0.05% and 10% by         volume.

Advantageously, the composition is environmentally friendly, results in greater than 90% sand removal and is resistant to common drilling contaminants such as solids, gypsum, lime and salt inter alia.

Perhaps one of the most important features of the composition is ease with which the emulsion is broken to provide the oil and water as discrete phases. By enzymatic action, the emulsion is de-emulsified and this has been observed over a wide temperature range. In fact, the emulsion is broken in the absence of energy input, a significant feature.

A still further object of one embodiment of the present invention is to provide a method of recovering oil from tar sands containing tar, oil and sand, comprising:

-   -   providing a composition containing a polymer, solvent for         solving oil and tar from said tar sands and an emulsifier;     -   mixing compounds of said composition;     -   treating the tar sands with the composition to remove sand from         the tar sands;     -   forming an emulsion with oil contained in treated tar sands         where the emulsion is oil in water emulsion; and     -   de-emulsifying, under either energized or static conditions, the         emulsion to release the oil as a separate phase from the water.

The composition in use has easily maintainable rheology and filtration control over a broad range of downhole operations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following experiments are representative of the invention methodology and set forth experimental details in respect of the solution of the components of which the polymer system was made.

Experiment 1

An organic natural surfactant (Ho Flo) was evaluated in Kim Mud for its effect on tar sand. Testing was done at 30° C. It was found that Ho Flo at 0.1L/m³ in Kim Mud improves the clumping of tar sand oil and prevents the stickiness of the oil to the testing container.

Experiment 2

As an extension of Experiment No. 1, further testing was performed on Ho Flo surfactant in Kim Mud regarding its ability to prevent the tar sand oil from sticking to steel. Lab results showed no apparent sticking of oil to steel in straight Kim Mud. Consequently, Ho Flo was not required.

Experiment 3

Solubility of two tar sand samples was tested in DMO 100 at room temperature (23° C.) and 35° C. At 23° C., DMO solubilized most of the tar leaving clean and freely moving sand. Temperature elevation to 35° C. resulted in higher solubility and complete removal of the tar from sand.

Experiment 4

Four lubricants were tested in Stable K (organic amine) mud to select the one with the least effect on tar sand. Testing was done at 23° C. and lubricant concentration of 1.5 and 3.0 kg/m³.

EZ Drill and EZ Drill II (biodegradable organic oils) appeared to soften the tar sand, although no obvious sign of dissolvability of tar sand was noticed.

Tork-trol II and EZ Slide produced no change in the tar sand appearance.

Experiment 5

Stable K mud, Gel Chem mud, Stable K/K₂SO₄ mud and Polymer mud were evaluated for their ability to prevent blinding/sticking of bitumen from tar sands to screens. The testing temperature ranged from 5 to 20° C. and the screens used were 50, 70, 84 and 110 mesh. The Stable K mud was tested at 25 and 30° C. as well.

No blinding/sticking of bitumen to any screen occurred with any of the muds. The bitumen behaved the same in each mud.

Experiment 6

Various additives were tested in Polymer mud, Stable K mud and K₂SO₄/Gel mud to select the best combination that water wets the shaker screen and prevents sticking of tar sands to screen.

Drilltreat at 5 L/m³ was the best additive improving the water wetting ability of all muds. K₂SO₄ worked similar in a Gel mud and less in Polymer mud. Q'Flow (Glycol) produced a softening of tar sands and dissolved some of the tar.

The second part of testing searched for an effective solvent of tar sands. Diesel, DMO 100 and HT-40N mixture of severely hydrotreated and hydrocracked base oil were tested at 23° C. The best solvent of tar from sand was Diesel with HT-40N being second best, DMO 100 was not found effective in removing the tar.

Experiments 7-9 represent lab work performed to develop a drilling fluid that solved the problems associated with drilling through tar sands. Thus, tar sand stickiness to equipment and shaker screen blinding was prevented with the new drilling fluid by removing the tar from the sand.

The idea behind the new drilling fluid was to formulate a direct emulsion where the external phase is water based and the internal phase is the organic solvent that removes the tar. Thus, the drilling fluid works by using the internal phase to clean the sand and keeping the removed oil in emulsion as fine drops. The emulsion is of loose structure and is readily broken or demulsified.

Experiment 7

The experiment relates to tests performed to select the organic solvent.

In order to find the best tar remover, over 50 products were tested at various concentrations. Q'Clean™ (a mixture of petroleum hydrocarbons) was selected as the best tar remover. Generally speaking, the product comprises hydrogenated heavy petroleum naphtha together with an organic solvent.

While Q'Clean™ was found as the tar remover and internal phase in the new drilling fluid, the external (continuous) phase selected was a Polymer/Stable K fluid.

No emulsifiers were required. Testing showed that emulsifiers had an adverse reaction by creating too small a drop of Q'Clean™ in the drilling fluid reducing its ability for cleaning the sand.

The new drilling fluid, Polymer/Stable K/Q'Clean™ was effective in removing the tar from the sand over a large range of temperatures, namely 5-30° C.

Experiment 8

This experiment sets forth work done to evaluate the performance of drilling fluid on a different sample of tar sands.

The Polymer/Stable K/Q'Clean™ fluid was tested at temperatures between 5 and 30° C. on tar sand from ECR 3B 102 Leismer LSD 2/13-16-76-6w4. Testing confirmed that Polymer/Stable K/Q'Clean™ fluid worked very well; the tar sand was cleaned at the temperature range indicated.

Experiment 9

This experiment related to developing the optimum formulation for the drilling fluid. The objective was to find the drilling fluid that dissolved and incorporated the tar, was least affected by contaminants and could be easily disposed of at the end of the well.

The project had 3 parts:

-   -   designing and testing for the optimum formulation of drilling         fluid with regards to tar removing ability;     -   testing the likely contaminants on the fluid to see if any fluid         formulation adjustment is required; and     -   testing for emulsion breaking and oil phase separation for fluid         disposal at the end of the well.

A new drilling fluid formulation containing Polymers/sized Calcium Carbonate/Q'Clean™ was designed and tested. Various viscosifiers were tested at different concentrations with regards to mud rheology, cleaning ability and effect on emulsion breaking.

The following fluid formulation was selected fin its good rheology, fluid loss and tar sand cleaning ability:

PolyTar ™ System Kelzan XCD 0.75 kg/m³ (polysaccharide gum) Staflo R 2 kg/m³ (sodium carboxymethyl cellulose) Starpak DP 6 kg/m³ (modified starch) Calcarb 325 10 kg/m³ (calcium carbonate) Calcarb 0 10 kg/m³ (calcium carbonate) Caustic Soda pH 10 Q'Clean ™ 5% v/v (mixture of petroleum hydrocarbons)

Data illustrating the effectiveness will be presented herein after.

Contaminants testing on the drilling fluid showed minimal effects on its rheology and cleaning ability. Thus, gypsum and salt (NaCl) produced a moderate decrease in fluid rheology. The cleaning ability was affected only by salt; slightly reduced from 96% wt. to 80% wt. Solids contamination was simulated by adding 6% v/v tar sand to the drilling fluid already containing 5% v/v tar sand. The fluid behaved very well, cleaning 26% wt. tar sand off of the extra 6% v/v tar sand added.

After finding the fluid formulation and testing the contaminants, the environmental aspect of fluid development was reviewed. At the end of the well, the drilling fluid is a direct emulsion that contains as the internal phase (oil phase) the solvent (Q'Clean™) and the dissolved tar. In order to be able to dispose of the drilling fluid, the emulsion has to be broken and oil phase has to be separated and removed.

Breaking the emulsion of PolyTar™ System was attempted in three ways:

-   -   1. By making use of chemical demulsifiers. Eight demulsifiers         were tested with no good results;     -   2. Making use of non-emulsifiers (two products) in the mud         formulation to prevent the forming of a stable emulsion; and     -   3. Using a polymer breaker (four products, enzymes and bleach)         to reduce the fluid viscosity and speed up the oil separation.

Q'Break™ (citric acid and amylase) (enzyme) at concentration of 2 kg/m³ is the best product to help with emulsion breaking and oil separation from the drilling fluid. It produces a fast reduction in mud viscosity, the emulsion breaks easily and the oil (Q'Clean™+Tar) separates on top of fluid. After the treatment with Q'Break™ 2 kg/m³ and 24 hours static at 22° C., the oil left in emulsion in the mud was only 0.47% v/v. Most of the oil phase (Q'Clean™ and dissolved Tar) was separated from the mud as a top layer and could be skimmed off.

Q'Break™ is an enzyme that works well at low temperatures, however, higher concentrations are recommended. Also, the product is safe and environmentally friendly.

A new approach to tar sand drilling resulted in development of a new drilling fluid addressing specific problems encountered in SAGD drilling projects.

The new drilling fluid was designed to solve the problem of tar sand stickiness by removing the tar from the sand. Lower toxicity and lower cost were pursued as attributes of the new drilling fluid designed.

Tables 1 and 2 set forth data and observations noted.

In respect of the drilling fluid composition, the following procedure was observed.

-   -   Various additives at various concentrations were added to water         to examine the capacity to remove tar and clean the sand.     -   200 ml of the testing fluid received 20 g of tar sands.     -   The mixture was mixed on a Barnant mixer for 30 minutes at room         temperature. The range of temperature for the testing was         between 5° C. and 30° C.

Table 1 tabulates the data and observations noted

TABLE 1 Fluid Additive selection Additive & concentration in water WTS, g Visual observations Blank (water) 19.580 Tar sands appeared unchanged. Fluid phase is clear and clean. PAW 2315 @ 1% v/v 19.660 Tar sands appeared unchanged. Fluid phase is clear. PAW 2315 @ 3% v/v 20.125 There is a very small amount of clean sand. The tar sand left is broken into smaller pieces; however, they remained hard. Fluid phase contains suspended small oil drops cleaned off the sand. PAW 3900 @ 1% v/v 20.138 Similar to PAW 2315 @ 1% v/v. PAW 3900 @ 3% v/v 20.632 There is a very small amount of clean sand. The tar sand left seems to remain in same size pieces; however, they remained hard. Fluid phase contains suspended small oil drops cleaned off the sand. WAW 3917 @ 3% v/v 19.883 Similar to PAW 2315 @ 1% v/v. WAO 3919U @ 3% v/v 20.281 Works well. Most sand is loose and fairly clean and the fluid phase is dark coloured. There are a few small soft pieces of tar sand left on the bottom of the beaker. WAO 3919U @ 1% v/v 20.002 Similar to PAW 3919U @ 3% v/v. Just not quite as effective in cleaning the sand. Beta Cyclod. @ 5 kg/m³ 20.420 There is a very small amount of clean sand. The tar sand left seems to remain in same size pieces. Fluid phase has a thin oily film on top. There are lost of small tar sand particles. Beta Cyclod. @ 10 kg/m³ 21.940 No significant improvement. Beta Cyclod. @ 20 kg/m³ 20.600 No significant improvement. Noticeable is the fact that 20 kg/m³ appears to be above its solubility. Cut Clean @ 1% v/v 20.283 There is a large amount of clean sand and large pieces of tar sand left. The fluid phase is clear with no suspended solids. It has an oily film and a ring at the surface. Cut Clean @ 2% v/v 20.146 The tar sand is completely broken down. On top of the sand layer there is a layer of large oil globules separated when agitation ceased. The fluid phase is cloudy, tan, with the odd suspended globule of oil and a thick layer of oil on top. Cut Clean @ 3% v/v 19.948 The sand is completely entrapped in what appears to be a water in oil emulsion on the bottom of the beaker. This very viscous layer with a gel like consistency is easily moved with agitation. The fluid phase is similar to the one above. Mudd Lite @ 2% v/v 20.885 Tar sands appeared unchanged. Fluid phase is tan in colour and has a layer of foam on top. Mudd Lite @ 6% v/v 19.962 Similar to Mudd Lite @ 2% v/v. DH6-115-2 19.802 Tar sands appeared unchanged. Fluid phase is clear. E X107 @ 3% v/v 20.800 Tar sands appeared unchanged. Fluid phase is clear. E X1501 @ 3% v/v 20.670 There is a very small amount of clean sand. The tar sand left seems to remain in same size pieces. In water, this additive coagulated in a cream-yellow layer that separates on top of the fluid phase when at rest. E XA923 @ 3% v/v 20.791 Tar sands appeared unchanged. Fluid phase is clear. E X1033 @ 3% v/v 19.703 It broke the large tar sand pieces into small ones but there is no clean sand. S DN82 @ 3% v/v 20.799 The sand is completely entrapped in what appears to be a water in oil emulsion on the bottom of the beaker. The liquid phase above this bottom layer is clean and clear. E X1557 @ 3% v/v 19.600  ~75% of tar sand is completely clean. The rest of tar sand is in pieces looking unchanged. Under the microscope can see the oil in water emulsion that has a dark colour. There is a thin film of oil on top of fluid phase. E X1557 @ 1% v/v 20.557 Similar to above test, just that on the sand grains are not quite as clean. E X1557@ 5% v/v Same as @ 3% v/v. E X 606 @ 3% v/v 20.903 There is a very small amount of clean sand. The tar sand left seems to remain in same size pieces. The fluid phase is light tan in colour and contains few tar particles suspended. E X 109 @ 3% v/v 19.282  ~75% of tar sand is completely clean. The rest of tar sand is in pieces looking unchanged. Under the microscope can see the fluid as oil in water emulsion that has a dark colour. There is a thin film of oil on top of fluid phase. E X 109 @ 5% v/v 20.104 Same as @ 3% v/v. S DN71 @ 3% v/v 20.120  ~50% of sand is partially clean and the other 50% is left unchanged in tar sand pieces. The fluid phase is oil in water emulsion. S DN120 @ 3% v/v 20.322 There is less than 1% of clean sand. The tar sand left seems to remain in same size pieces. The fluid phase is clean and clear. S DN114 @ 3% v/v 19.820 As above S DN121 @ 3% v/v 20.026 ~15-20% of sand is clean. The rest appears unchanged. The fluid phase is milky-gray in colour. S DN87 @ 3% v/v 20.735  ~75% of sand is completely clean. The rest of tar sand is in fairly small pieces. Under the microscope can see the fluid as oil in water emulsion that has a dark colour. S DN87 @ 3% v/v 20.610 Some improvement from 3% v/v, however, there still are a few tar sand pieces left. S DN76 @ 3% v/v 21.028 Most of tar sand (~75%) is a flowing sludge on the bottom of beaker. There are a few pieces of tar sand DT78 @ 3% v/v 20.782 ~80-90% of sand is fairly clean but the oil is not emulsioned and just lays and sticks to the sand layer. DG56 @ 3% v/v 20.980 There is less than 1% of clean sand. The tar sand left seems to remain in same size pieces. The fluid phase is clean and clear. M38 @ 3% v/v 20.853  ~50% of sand is fairly clean and the other 50% is left small tar sand pieces. The fluid phase is oil in water emulsion. M150 @ 3% v/v 19.320  ~50% of loose sand, dark, still coated with oil. The rest of tar sand seems to remain in same size pieces. The fluid phase is dark M192 @ 3% v/v 20.962  ~75% of tar sand is completely clean. The rest of tar sand is in pieces looking unchanged. Under the microscope can see the oil in water emulsion that has a dark colour. There is a thin film of oil on top. M192 @ 5% v/v 20.042 Some improvement from 3% v/v, however there still are a few tar sand pieces left. M187 @ 3% v/v 20.178 ~15-20% of sand is clean. The rest appears unchanged. The fluid phase is tan in colour. Solvent @ 5% v/v 19.314  ~80% of sand is loose, free flowing but still covered by oil material P2-181-9 @ 1% v/v 20.386  ~50% of sand is fairly clean and the other 50% is left small tar sand pieces. The fluid phase is an emulsion. P2-181-11B @ 1% v/v 20.408 ~15-20% of sand is clean. The rest appears unchanged. P2-181-15B @ 1% v/v 20.560  ~50% of sand is fairly clean and the other 50% is left small tar sand pieces. The fluid phase is an emulsion. P2-181-19B @ 1% v/v 21.300 Complete balling of tar sands that became soft (it incorporated water) and sticky. P2-181-16B @ 1% v/v 21.107 ~15-20% of sand is clean. The rest appears unchanged. P2-181-21B @ 1% v/v 20.144 ~15-20% of sand is clean. The rest of tar sand is soft and sticky. Travis 2095 @ 1% v/v 21.893  ~5% of sand is clean. The rest appears unchanged. Travis 2704 @ 1% v/v 20.982 Tar sands appeared unchanged. Fluid phase is clear. Drilling Fluid selection - Polymer/Stable K system Additive & concentration In drilling fluid WTS, g Visual Observations Blank (Poly./Stable K) E XZ1557 @ 1% v/v 20.634 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. E XZ1557 @ 3% v/v 20.049  ~40% of tar sand remained on the 30 mesh screen as small and large pieces. Dark fluid phase of oil in water emulsion. Xylene/Isopropanol 20.250 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. @ 3% v/v Diesel @ 3% v/v 20.975 There is a small amount of loose sand. Tar sand left remained in same size pieces. Fluid phase is emulsion with suspended tar particles. Diesel @ 10% v/v 19.580 Most solids are loose, still covered by oil and flowing. Diesel @ 10% v/v + XZ1557 20.078 Tar sands appeared unchanged. The oil is emulsioned as extremely small drops that could @ 3% v/v not contact the tar sands and is fairly clean. BDD100 @ 3% v/v 20.980 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. BDS300 @ 3% v/v 19.047 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. BDS200 @ 3% v/v 20.382 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. E X1577 @ 3% v/v 20.490 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. E X1421 @ 3% v/v 20.195 It produced rapid precipitation-coagulation of the Polymer/Stable K system. E X1262 @ 3% v/v 20.728 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. E X1667 @ 3% v/v 20.801 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. DWB-1-5 @ 3% v/v 20.221 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. DWB-1-9 @ 3% v/v 20.453 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. DWB-1-6 @ 3% v/v 20.735 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. DWB-1-7 @ 3% v/v 20.466 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. DWB-1-8 @ 3% v/v 19.952 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. Solvent @ 3% v/v + XZ1557 20.942 Some clean sand grains seen under microscope. Most tar sand is left uncleaned as small @ 1% v/v pieces. Solvent @ 10% v/v 20.631 Cleaned most of sand. Mixture is poured on a 30 mesh screen. ~10% of tar sand remained on the screen. Can see the clear - clean sand grains suspended in the fluid and the dark oil drops. Fluid phase is very dark due to the dissolved oil. Solvent @ 10% v/v + Rev 20.17  <5% of tar sand left on the 30 mesh screen as small and soft pieces. Dark fluid phase Dust 4% v/v containing almost completely clean sand. Solvent @ 7% v/v + Rev 20.353  ~5-7% of tar sand left on the 30 mesh screen. The rest as above. Dust 4% v/v M192 @ 5% v/v 20.824  ~70% of tar sand remained on the 30 mesh screen as small and large pieces. Dark fluid phase. Amodrill 1400 @ 10% v/v 20.560  ~30% of tar sand remained on the 30 mesh screen as small and large pieces. Dark fluid phase. Emulam D30 @ 5% v/v 20.106 ~100% of tar sand remained on the 30 mesh screen as unchanged small and large pieces. Cut Clean @ 5% v/v 20.929  ~30% of tar sand remained on the 30 mesh screen as small and large pieces. Dark fluid phase. Drilling Fluid selection - Gel Chem system Additive & concentration in drilling fluid WTS, g Visual Observations Blank (Gel Chem sys.) 20.651 Tar sands appeared unchanged. Fluid phase contains small tar particles suspended. Tar Solvent @ 10% v/v 20.920  ~20% of tar sand remained on the 30 mesh screen as small and large pieces. Dark fluid phase with fairly clean sand suspended. Tar Solvent @ 10% v/v + Rev 20.700 As above. Dust @ 4% v/v Additive concentration and mixture temperature WTS, g Visual Observations Tar Solvent @ 20% v/v- 20.878  ~10% of tar sand left on the 30 mesh screen as small and soft pieces. Dark fluid phase 5° C. containing almost completely sand. Tar Solvent @ 10% v/v- 19.968  ~50% of tar sand left on the 30 mesh screen as small and soft pieces. Dark fluid phase. 10° C. Tar Solvent @ 15% v/v- 20.261  ~20% of tar sand left on the 30 mesh screen as small and soft pieces. Dark fluid phase. 10° C. Tar Solvent @ 20% v/v- 20.325  ~10% of tar sand left on the 30 mesh screen as small and soft pieces. Dark fluid phase 10° C. containing almost completely sand. Tar Solvent @ 15% v/v- 20.380  ~20% of tar sand left on the 30 mesh screen as small and soft pieces. Dark fluid phase. 15° C. Tar Solvent @ 20% v/v- 20.375  ~10% of tar sand left on the 30 mesh screen as small and soft pieces. Dark fluid phase 15° C. containing almost completely sand. Tar Solvent @ 10% v/v- 20.713  ~5% of tar sand left on the 30 mesh screen as small and soft pieces. Dark fluid phase 20° C. containing almost completely sand. Tar Solvent @ 10% v/v- 20.532 As above 25° C. Tar Solvent @ 10% v/v- 20.342  ~3% of tar sand left on the 30 mesh screen as small and soft pieces. Dark fluid phase 30° C. containing almost completely sand.

In connection with the fluid testing, the following procedure was involved.

-   -   200 mL of drilling fluid, discussed herein previously, was         placed in a beaker to which 20 g of Tar Sands was added. This         was mixed on a Barnant mixer for 30 minutes at room temperature.         The mixture was passed through a 30 mesh screen.

The test was repeated in a temperature range of between 5 and 30° C.

TABLE 2 Tar sands from 397.4 m depth - Drilling fluid testing Solvent concentration in drilling fluid and test temperature WTS, g Visual Observations 15% v/v Solvent & 5° C. 20.450 ~15-20% of tar sand left on the 30 mesh screen (small and large pieces) and a significant amount of clean large sand grains (~3 mm diameter). Dark fluid phase containing completely clean sand 20% v/v Solvent & 5° C. 19.781 ~10% of tar sand left on the 30 mesh screen (small and large pieces) and a significant amount of clean large sand grains (~3 mm diameter). Dark fluid phase containing completely clean sand 10% v/v Solvent & 10° C. 19.968 ~20% of tar sand left on the 30 mesh screen as various size pieces. The rest is as above. 15% v/v Solvent & 10° C. 20.261 ~15% of tar sand left on the 30 mesh screen as various size pieces. The rest is as above. 20% v/v Solvent & 10° C. 20.371  ~7-10% of tar sand left on the 30 mesh screen as small and soft pieces. The rest is as above. 10% v/v Solvent & 15° C. 20.482 ~15% of tar sand left on the 30 mesh screen as various size pieces. The rest is as above. 15% v/v Solvent & 15° C. 20.037 ~15% of tar sand left on the 30 mesh screen as various size pieces. The rest is as above. 20% v/v Solvent & 20° C. 20.389  ~3% of tar sand left on the 30 mesh screen as small size pieces. The rest is as above.  0% v/v Solvent & 20° C. 20.253 ~80% of tar sand left on the 30 mesh screen as small size pieces. The solids that passed through the screen are suspended in the fluid and consist of tar sands and heavy oil particles. 10% v/v Solvent & 20° C. 20.135  ~7-10% of tar sand left on the 30 mesh screen (small and large pieces) and a significant amount of clean large sand grains (~3 mm diameter). Dark fluid phase containing completely clean sand 10% v/v Solvent & 25° C. 20.185  ~5% of tar sand left on the 30 mesh screen as various size pieces. The rest is as above. 10% v/v Solvent & 30° C. 20.019 No tar sand left on the 30 mesh screen. The only solids left on screen are the clean large sand grains (~3 mm diameter). Dark fluid phase containing completely clean sand. Note: WTS—weight of tar sands.

In all the above tests where the new drilling fluid was used (all except sample with 0% v/v Solvent), the fluid phase was an oil in water emulsion. The oil drops had a good size (not too small, not too big) and were dark colored due to the tar having been stripped off the sand.

The core sample of tar sands used to perform the above testing showed very small pieces of completely clean solids (shale like). These clean solids were avoided when tar sand samples were removed from the core during testing.

Tables 3 through 22 tabulate data for different polymer systems together with specific listing for each.

As set forth herein previously, having listed the necessary components for the polymer system, ranges for effectiveness were required for determination. The following two polymer systems were tested

Polymer System A Polymer System B Additive Concentration Additive Concentration Kelzan 1.5 kg/m³  Kelzan 2 kg/m³ XCD ® XCD ® Staflo ® R  2 kg/m³ Staflo ® R 2 kg/m³ Starpak ®  6 kg/m³ Starpak ® 6 kg/m³ DP DP Calcarb 10 kg/m³ Calcarb 10 kg/m³  325 325 Calcarb 0 10 kg/m³ Calcarb 0 10 kg/m³  Caustic pH 10 Caustic pH 10 Soda Soda Q/C = Q'Clean

TABLE 3 Mud Formulation Testing - Rheology and API fluid loss at 23° C. Gels, PV, YP, FL, Formulation 600 rpm 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm Pa cP Pa mL A  65 47 40 30 23 17  8  7 3.5/4.0 18 14.5 13.8 A + 2.5% Q'C  66 49 41 30 24 18  8  7 3.5/4.0 18 16.0 12.0 A + 5% Q'C  70 52 43 32 25 18  9  8 4.0/4.5 18 17.0  9.8 A + 10% Q'C  71 52 43 32 25 19  9  8 4.5/4.5 19 16.5  8.3 B 101 78 67 48 40 30 12 10 4.5/5.0 23 27.5 11.2 B + 2.5% Q'C 105 81 69 52 41 30 13 11 5.0/5.5 24 28.5 11.0 B + 5% Q'C 110 84 72 54 43 31 14 11 5.5/5.5 26 29.0 12.4 B + 10% Q'C 115 89 75 57 46 33 15 12 6.0/6.0 26 31.5  9.0

TABLE 4 Tar Sand Cleaning at 23° C. Weight, g Tar sand Fluid Tar Residue Residue cleaned, Formulation sand Dish & Dish >30 mesh % wt. A 27.131 1.060 23.013 21.953 19.1 A + 2.5% Q'C 27.122 1.000 7.890 6.890 74.6 A + 5% Q'C 27.300 1.033 2.112 1.079 96.0 A + 10% Q'C 27.644 1.004 1.671 0.667 97.6 B 27.233 1.039 23.474 22.435 17.6 B + 2.5% Q'C 27.473 1.038 8.375 7.337 73.3 B + 5% Q'C 27.457 1.031 2.718 1.687 93.9 B + 10% Q'C 27.295 1.038 2.273 1.235 95.5

TABLE 5 Contaminants Testing on the PolyTar System (PTS = A + 5% Q'C). Rheology at 23° C. Gels, PV, YP, Sample 600 rpm 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm Pa cP Pa PTS 64 47 39 28 23 16 8 6 3.0/3.5 17 15 PTS + 5 kg/m³ 48 35 29 20 16 12 5 4 2.5/2.5 13 11 Gypsum PTS + 1 kg/m³ Lime 64 47 39 28 23 16 8 6 3.0/3.5 17 15 PTS + NaOH for pH12 62 46 38 28 22 15 7 5 3.0/3.0 16 15 PTS + 5 kg/m³ NaCl 56 41 34 24 19 13 6 5 2.5/3.0 15 13 PTS + 10 kg/m³ NaCl 54 39 32 23 18 13 6 5 2.5/3.0 15 12 PTS + 20 kg/m³ NaCl 49 35 29 21 16 11 5 4 2.0/2.5 14 10.5 PTS + 6% vol. Tar 72 52 42 31 24 18 9 6 3.0/3.5 20 16 Sand

TABLE 6 Contaminants Testing on the PolyTar System (PTS). API fluid loss FL, Sample mL PTS 10 PTS + 5 kg/m³ Gypsum 9.5 PTS + 1 kg/m³ Lime 10 PTS + 5 kg/m³ NaCl 9.5 PTS + 10 kg/m³ NaCl 9 PTS + 20 kg/m³ NaCl 8 PTS + 6% vol. Tar Sand 6

TABLE 7 Tar Sand Cleaning in contaminated fluid at 23° C. - 5% vol. Tar Sand in the Fluid Sample Tar Weight, g sand Tar Residue Residue cleaned, Fluid Sample sand Dish & Dish >30 mesh % wt. PolyTar System (PTS) 27.300 1.033 2.112 1.079 96.0 PTS + 5 kg/m³ Gypsum 27.611 1.002 2.882 1.880 93.2 PTS + 1 kg/m³ Lime 27.273 1.027 2.527 1.500 94.5 PTS + 5 kg/m³ NaCl 27.458 0.998 5.720 4.722 82.8 PTS + 10 kg/m³ NaCl 27.397 1.004 6.278 5.274 80.7 PTS + 20 kg/m³ NaCl 27.315 1.004 6.425 5.421 80.2 PTS + 6% vol. Tar Sand 27.289 1.020 21.099 20.079 26.4

TABLE 8 PolyTar System/Dissolved Tar Emulsion Breaking at 23° C. - Removal of dissolved tar. Conc., Demulsifier L/m³ Notes on emulsion behaviour None Oil drops are small but visible with naked eye. The oil in water emulsion is stable. it does not break in over 8 hours. After 24 hours there is a very small amount of free oil on top of fluid. T2001 1 Oil drops are not visible with naked eye. Under the microscope they look 2-3 times smaller than 2 they were initially. The oil in water emulsion became more stable. It does not break in over 24 hours. There is no free oil on top of fluid. T2005 1 Oil drops are not visible with naked eye. Under the microscope they look 2-3 times smaller than 2 they were initially. The oil in water emulsion became more stable. It does not break in over 24 hours. There is no free oil on top of fluid. T2007 1 Oil drops are not visible with naked eye. Under the microscope they look 2-3 times smaller than 2 they were initially. The oil in water emulsion became more stable. It does not break in over 24 hours. There is no free oil on top of fluid. T2508 1 Oil drops are not visible with naked eye. Under the microscope they look 2-3 times smaller than 2 they were initially. The oil in water emulsion became more stable. It does not break in over 24 hours. There is no free oil on top of fluid. NE 125 0.5 Oil drops are small but visible with naked eye. The oil in water emulsion is stable. It does not 1 break in over 8 hours. After 24 hours there is a very small amount of free oil on top of fluid. 2 NE 723 0.5 Oil drops are small but visible with naked eye. The oil in water emulsion is stable. It does not 1 break in over 8 hours. After 24 hours there is a very small amount of free oil on top of fluid. 2

TABLE 9 PolyTar System/Dissolved Tar Emulsion - Preventing forming a stable emulsion using non-emulsifiers (23° C.). Conc., Non-emulsifier L/m³ Notes on emulsion behaviour None Oil drops are small but visible with naked eye. The oil in water emulsion is stable. It does not break in over 8 hours. After 24 hours there is a very small amount of free oil on top of fluid. NE 125 1 Oil drops are not visible with naked eye. Under the microscope they look 2-3 times smaller than 2 they were initially. The oil in water emulsion became more stable. It does not break in over 24 hours. There is no free oil on top of fluid. NE 723 1 Oil drops are not visible with naked eye. Under the microscope they look 2-3 times smaller than 2 they were initially. The oil in water emulsion became more stable. It does not break in over 24 hours. There is no free oil on top of fluid.

TABLE 10 Tar Sand Cleaning at 23° C. - PTS cleaning ability when using non-emulsifiers at 1 L/m³. Weight, g Tar sand Tar Residue Residue cleaned, Non-emulsifier sand Dish & Dish >30 mesh % wt. NE 125 27.655 1.036 13.601 12.565 54.6 NE 723 27.504 1.000 8.898 8.898 67.6

TABLE 11 Viscosifier selection to prevent forming a stable PolyTar System/ Dissolved Tar Emulsion - Polymer (Viscosifier) Testing in PolyTar System - Rheology at 23° C. Gels, PV, YP, Viscosifier kg/m³ 600 rpm 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm Pa cP Pa Kelzan XCD 1.5 70 52 43 32 25 18 9 8   4/4.5 18 17 Biovis 1.5 54 37 29 18 13  8 3 2   1/1.5 27 5 Biovis 3 73 53 44 33 27 20 10  8 4.5/6.5 20 16.5 Geovis XT 1.5 71 51 42 32 25 19 10  9 5/7 20 15.5 HEC 1.5 92 70 58 43 33 23 9 7 3.5/3.5 22 24 Xanvis 1.5 60 43 36 26 20 15 7 6   3/3.5 17 13

TABLE 12 Tar Sand Cleaning at 23° C. - PTS cleaning ability when using viscosifiers and concentrations above mentioned. Weight, g Tar sand Tar Residue Residue cleaned, Viscosifier sand Dish & Dish >30 mesh % wt. Kelzan XCD 27.300 1.033 2.112 1.079 96.0 Biovis - 1.5 27.345 1.009 5.076 4.067 85.1 Biovis - 3 27.474 1.033 3.398 2.365 91.4 Geovis XT 27.343 1.020 4.354 3.334 87.8 HEC 27.456 1.031 9.140 8.109 70.5 Xanvis 27.333 1.002 4.638 3.636 86.7

TABLE 13 Viscosifier selection to prevent forming a stable PolyTar System/Dissolved Tar Emulsion - Testing at 23° C. Conc., Viscosifier kg/m³ Notes on emulsion behaviour within 6 hours Kelzan XCD 1.5 The oil in water emulsion is less stable. Emulsion is slowly breaking. There is a bit of free oil on top of fluid after 6 hours. This sample looks the best. Biovis 3 The oil in water emulsion is stable. No sign of emulsion breaking in 6 hours. There is no free oil on top of fluid. Geovis XT 1.5 The oil in water emulsion is stable. No sign of emulsion breaking in 6 hours. There is no free oil on top of fluid. HEC 1.5 The oil in water emulsion is stable. No sign of emulsion breaking in 6 hours. There is no free oil on top of fluid. Xanvis 1.5 The oil in water emulsion appears less stable. Emulsion is slowly breaking. There are traces of free oil on top of fluid after 6 hours. This sample is the next best.

TABLE 14 Polymer Breaker Testing on PTS containing Kelzan XCD @ 1.5 kg/m³ - Rheology after 24 hours @ 23 ° C. Breaker & conc., Gels, PV, YP, kg/m³ 600 rpm 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm Pa cP Pa None 66 48 41 30 24 17 8 6   3/3.5 18 15 Q'Break, 2 41 28 22 15 11  8 4 3 1.5/1.5 13 7.5 Chembreak HC, 3 41 27 22 15 11  8 3 2   1/1.5 14 6.5 Chembreak EBS, 3 52 38 31 22 17 12 6 5 2.5/3   14 12 Chembreak EBS, 3* 48 34 28 20 16 11 5 4 2/2 14 10 Bleach, 5 L/m³ 26 17 13  9  7  5 2 2 1/1  9 4 Note: *sample contains 5,000 ppm Cl as NaCl.

An adjusted polymer system was then reviewed.

Adjusted PolyTar System formulation (less viscosifier) Additive Concentration Additive Concentration Kelzan .75 kg/m³  Xanvis ® 1 kg/m³ XCD ® Staflo ® R  2 kg/m³ Staflo ® R 2 kg/m³ Starpak ®  6 kg/m³ Starpak ® 6 kg/m³ DP DP Calcarb 10 kg/m³ Calcarb 10 kg/m³  325 325 Calcarb 0 10 kg/m³ Calcarb 0 10 kg/m³  Caustic pH 10 Caustic pH 10 Soda Soda Q' Clean 5% vol. Q' Clean 5% vol.

TABLE 15 PolyTar System/Dissolved Tar Emulsion (5% vol. Tar Sand in the mud) - Rheology at 23° C. Gels, PV, YP, Viscosifier kg/m³ 600 rpm 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm Pa cP Pa Kelzan XCD 0.75 58 42 34 24 18 12 5 4 2/2 16 13 Xanvis 1 62 46 38 27 21 15 6 5 2.5/3   16 15

TABLE 16 Tar Sand Cleaning at 23° C. - PTS cleaning ability when using viscosifiers and concentrations above mentioned. Weight, g Tar sand Tar Residue Residue cleaned, Viscosifier sand Dish & Dish >30 mesh % wt. Kelzan XCD 27.397 1.059 4.116 3.057 88.8 Xanvis 27.512 1.040 5.076 4.378 84.1

TABLE 17 Polymer Breaker Testing on PTS containing Kelzan XCD @ 0.75 kg/m³ - Rheology after 2 hours @ 23° C. Breaker & conc., Gels, PV, YP, kg/m³ 600 rpm 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm Pa cP Pa None 58 42 34 24 18  12  5 4 2/2 16 13 Q'Break, 2 41 25 19 12 9 5 2 2 1/1 16 4.5 Chembreak HC, 3 27 17 13  8 5 4 1 1 0.5/0.5 10 3.5 Bleach, 5 L/m³ 56 36 27 17 13  8 3 2 1/1 20 8

TABLE 18 Polymer Breaker Testing on PTS containing Xanvis @ 1 kg/m³ - Rheology after 2 hours @ 23° C. Breaker & conc., Gels, PV, YP, kg/m³ 600 rpm 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm Pa cP Pa None 62 46 38 27 21 15 6 5 2.5/3   16 15 Q'Break, 2 44 28 22 14 10  7 3 2 1/1 16 6 Chembreak HC, 3 41 28 22 15 11  7 3 2 1/1 13 7.5 Bleach, 5 L/m³ 69 47 38 25 19 13 5 4   2/2.5 22 12.5

TABLE 19 Retort Test on PolyTar System/Dissolved Tar Emulsion (5% vol. Tar Sand in the mud) Sample from ½ height of emulsion Total in 250 mL graduated Retort content, % v/v Hydrocarbons Content cylinder after 24 hours Oil Water Solids (Core Labs), % v/v Blank (no ECA) 5 94 1 Q'Break 2 kg/m3 2 97 1 0.473 Q'Break 4 kg/m3 1 99 0 0.492

TABLE 20 Q'Break Testing at 23° C. (room) on PTS containing Kelzan XCD @ 0.75 kg/m3 - Rheology @ 23° C. Q'Break Gels, PV, YP, kg/m³ 600 rpm 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm Pa cP Pa None 58 42 34 24 18  12  5 4 2/2 16 13 2 kg/m³, after 2 hours 40 26 20 13 9 6 2 2 1/1 14 6 2 kg/m³, after 6 hours 36 23 18 11 8 5 2 1 0.5/0.5 13 5 2 kg/m³, after 24 hours 31 20 15 10 7 4 1 1 0.5/0.5 11 4.5 4 kg/m³, after 2 hours 39 25 20 13 9 6 2 2 1/1 14 5.5 4 kg/m³, after 6 hours 25 16 12  7 5 3 1 1 0.5/0.5  9 3.5 4 kg/m³, after 24 hours 20 12  9  6 4 3 1 1 0.5/0.5  8 2

TABLE 21 Q'Break Testing at 3° C. (fridge) on PTS containing Kelzan XCD @ 0.75 kg/m3 - Rheology @ 3° C. Gels, PV, YP, Q'Break, kg/m³ 600 rpm 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm Pa cP Pa None 74 52 43 30 23 16  7 5 2.5/3   22 15 2 kg/m³, after 3 hours 54 35 27 17 12 8 3 2 1/1 19 8 2 kg/m³, after 6 hours 40 25 19 12  9 5 2 1 0.5/0.5 15 5 4 kg/m³, after 2 hours 47 31 23 15 11 7 2 2 1/1 16 7.5 4 kg/m³, after 6 hours 38 24 17 11  8 5 2 1 0.5/0.5 14 5

TABLE 22 Emulsion Breaking using both Q'Break 2 kg/m3, let sit 3 hours then add demulsifier. Testing at 23° C. Conc., Demulsifier L/m³ Notes on emulsion behaviour - 250 mL sample in a graduated glass cylinder. None Emulsion is slowly breaking. There is a a layer of ~12 mL of very dark fluid on top after 3 hours. (Blank) Large oil drops form and accumulate towards top of fluid. After 48 hours the sample shows a very good oil separation. After 1 week there is the oil layer on top, clear water phase in the middle and solids layer on bottom. RD2069 1 Uppon mixing the RD2069 demulsifier, there was a stringy, gummy precipitate formed. Otherwise, the sample looks similar to the blank but having smaller oil drops accumulating towards the top. Demulsifier cannot be used due to chemical incompatibility with mud components (precipitation). T2005 1 Emulsion seems to very slowly break. There is a a layer of ~9 mL of very dark fluid on top with a definite separation from the lighter layer beneath after 3 hours. However, the rest of the fluid shows no sign of forming visible oil drops. After 48 hours the sample shows the least oil separation of all. After 1 week the is a layer of oil separated but the rest of the fluid is muddy and seems to contain traces of oil. JC91-6B 1 Emulsion is slowly breaking. There is a a layer of ~12 mL of very dark fluid on top after 3 hours. Large oil drops form and accumulate towards top of fluid. After 48 hours the sample shows a very good oil separation same as the blank. After 1 week there is the oil layer, clear water phase and solids layer similar to the blank.

Overall the polymer system containing the Kelzan XCD® in a concentration of 0.75 kg/m³ provided preferred rheology, fluid loss and cleansing of tar sands.

FIELD EXAMPLE

In January/February of 2004, six wells were drilled which used the PolyTar drilling fluid system in part of the drilling operation. The wells, located in 84-11 W4 in Alberta Canada, were horizontal in nature with the intermediate and main horizontal tar sands drilled with Polytar. The nature of sand was one of ˜23 v/v % bitumen contained within a ˜3 milliDarcy permeable poorly consolidated matrix.

Typical drilling conditions with Polytar are ˜400 meters of drilled 311 mm intermediate hole with casing set at 90° inclination from vertical. The 222 mm horizontal section was ˜600 meters in length. The following table highlights some of the Polytar drilling parameters as compared to other water-based muds used in the same 84-11 W4 area.

TABLE 23 Drilling Fluid Performance of Bitumen Laden Sands # of Average m Average Average Typical shaker System (year) wells drilled days to TD mud cost screen design K₂SO₄ polymer 4 1077 4.8 $27,755  38 * 38 * 38 (1998) K₂SO₄ polymer 6 1357 4.6 $10,280  38 * 38 * 38 (1998) KCl polymer 4 1505 8.8 $43,907  84 * 50 * 38 * 20 (2003) 140 * 110 * 84 * 50 Polytar 6 1078 3.9 $22,531 210 * 175 * 175 * 145 (2004) 210 * 210 * 180 * 145

The data shows that the Polytar system has been cost effective. Days to total depth were similar to the 6 well project using K₂SO₄ polymer and faster than the KCl polymer and K₂SO₄ polymer (4 wells) groupings. Drilling fluid costs for the Polytar system were also very competitive.

The average shaker screen sizes used on the Polytar system were much finer than those used on the other three system groupings. The potassium based systems, which used the larger screen sizes, were designed to carry the insoluble bitumen to surface intact. Typical of these potassium systems however, the bitumen accretes onto metallic surfaces. The shaker screens become less effective when accretion occurs, thus the need for larger screen openings.

The Polytar system solubilizes at least part of the bitumen into the drilling fluid system, thus eliminating accretion and increasing the efficiency of the shaker screens. As a result, cleaning of the drilling fluid system of drilled sand is improved. The sand collected from the shaker screen from the bitumen laden drilled solids contained typically less than 0.5% v/v oil.

The Polytar wells at 84-11 W4 employed centrifuges for additional drilling fluids cleaning functions. In general, the sand coming from the centrifuge underflow was clean enough to meet mix-bury-cover regulations within Alberta. The following tables set out the analyses received from centrifuge underflows at 700 m and 800 m measured depths.

TABLE 24 Hydrocarbon content from Centrifuge Underflows with Polytar Subsoil Density = 1820 kg/m3; soil:waste mix ratio 3:1 Waste Densities = 2020 and 1975 kg/m3 for 700 m and 800 m 700 m Analyses 800 m Analyses Closure Criteria Benzene 0 0 0.073 Toluene 0 0 0.86 Ethylbenzene 0 0 0.19 Xylenes 0 0 25 Fraction 1 0 0 260 Fraction 2 170 216 900 Fraction 3 169 212 800 Fraction 4 68 85 5600 Total HC's 407 513

The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims. 

1. An emulsifying drilling fluid for drilling in high oil viscosity tar sand formations containing water, tar, sand and oil entrained therein, comprising: a polysaccharide based polymer in an amount from between 0.05% and 5% by volume; an aliphatic hydrocarbon solvent in an amount from between 1% and 20% by volume for removing tar and oil from said tar sand; whereby an emulsion is formed having said water as an external phase and said aliphatic hydrocarbon as an internal phase of said emulsion, said emulsion containing said oil therein; and an enzyme based emulsion breaker in an amount from between 0.05% and 10% by volume for releasing said oil from said emulsion.
 2. The drilling fluid as set forth in claim 1, wherein said polymer is a polymer system.
 3. The drilling fluid as set forth in claim 2, wherein said polymer system includes at least polysaccharide gum, starch and PAC polyanionic cellulose. 